1. Field of the Invention
The present invention relates to a method of fabricating optical device caps, and more particularly, to a method of fabricating optical device caps so as to provide a good hermetic sealing, good penetrability and be able to package in wafer level.
2. Description of the Prior Art
In manufacturing processes, the microelectromechanical products with various kinds of applications and types will have different packaging processes. A wafer level package (WLP) is a semiconductor package in which the size of a finished package is similar to or slightly larger than a semiconductor die. After completion of all test processes and assembly processes or packaging processes, individual semiconductor packages are separated from a wafer having a plurality of semiconductor dies. Therefore WLP not only decreases a size of a memory module, but also satisfies a demand for high density.
Please refer to FIG. 1 through FIG. 3. FIG. 1 through FIG. 3 are schematic diagrams illustrating a method of fabricating optical device caps according to the prior art. As shown in FIG. 1, a wafer 10 is provided, and a plurality of through holes 12 is formed on the wafer 10 by a lithographic process and an etching process. Then, a glass wafer 14 is disposed on the wafer 10. As shown in FIG. 2, a heat conducting plate 16 is provided, and the wafer 10 is disposed on the heat conducting plate 16. As shown in FIG. 3, a plate 18 is provided, and the glass wafer 14 is disposed on the plate 18. The interface between the plate 18 and the glass wafer 14 is flat. Next, a voltage source 20 is provided, and an anode and a cathode of the voltage source 20 are respectively electrically connected to the wafer 10 and the plate 18. Then, an anodic bonding process is performed, and a high voltage is provided between the wafer 10 and the plate 18. Also, the heat conducting plate 16 heats the wafer 10 and the glass wafer 14 to a high temperature.
Please refer to FIG. 4, and FIG. 4 is a schematic diagram illustrating the reaction condition of the ions in the glass wafer 14 in the anodic bonding process. As shown in FIG. 4, when the wafer 10 and the glass wafer 14 are provided with a high voltage between them and a high temperature, the sodium oxide (Na2O) ions in the glass wafer 14 will be separated out the sodium ions (Na+) 22 and the oxygen ions (O2 −) 24. The oxygen ions 24 will be concentrated on the interface between the wafer 10 and the glass wafer 14, and then, the oxygen ions 24 will be reacted with the silicon atoms to form the silicon-oxygen (Si—Ox) covalent bonds so that the wafer 10 and the glass wafer 14 are bonded to each other (Si+2O2−→SiO2). The sodium ions 24 will move to the plate 18 and be combined with the electrons to form the sodium atoms (Na) (4Na++4e−→4Na). However, the sodium atoms will be attached to the surface of the glass wafer 14, and the sodium atoms cannot be removed by cleaning in the following process so that the optical device caps cannot have good penetrability. Therefore, the penetrability of the optical package device will also be affected so as to reduce the optical function of the optical device.